The present invention relates to a process for the production of open cell polyurethane foams.
Open cell foams have been utilized as a means for providing soft cushioning in a variety of applications in the automotive and furniture industries. In addition, these foams have been frequently employed within toys, athletic equipment, filters and sponges.
Such open cell polyurethane foams have traditionally been comprised of at least one polyol, an isocyanate, water, one or more surfactants, at least two catalysts which include a metallic catalyst as well as a tertiary amine catalyst, and, optionally, a blowing agent.
The blowing agent is employed in order to enhance the expansion of the foam which is obtained from the reaction of the water with the isocyanate. Traditionally, these blowing agents include chlorofluorocarbons such as Freon 11 or 12 and/or low boiling solvents such as methylene chloride.
However, certain problems associated with the use of chlorofluorocarbons, particularly environmental and public health problems, have led to the creation of an international agreement to reduce and eventually eliminate the use of these materials. Moreover, several states have already banned the use of methylene chloride due to health hazards which have been associated with its use. Thus, the art has been forced to look for alternative blowing agents.
One example of such a blowing agent has been liquid carbon dioxide as disclosed in U.S. Pat. Nos. 3,184,419 and 4,337,318.
U.S. Pat. No. 3,184,419 to Merriman, relates to a method for the production of polyurethane foam material. The method comprises the incorporation of a soluble inert gas under pressure in the liquified state into a liquid composition containing a prepolymer and a compound capable of reacting therewith to form a polyurethane foam composition. The carbon dioxide is introduced at a temperature below that which a substantial reaction between the prepolymer and the reactive compound takes place. The liquid composition is foamed by reducing the pressure of the mixer and raising the temperature of the foam to convert the composition to an elastomer.
Because this process requires the use of a prepolymer in the production of the foam, it can not be economically employed for large scale production. Moreover, this patent process requires cooling of the inert gas to aid in maintaining it in a liquid state which also adds to the expense of this procedure.
Doyle U.S. Pat. No. 4,337,318 relates to a "one shot process" for the production of a rigid, closed cell polyurethane foam utilizing liquid CO.sub.2 as a blowing agent. However, the closed cell foam differs greatly from the open cell foam of the present invention with respect to the compounds chosen for the isocyanates, polyols, cell forming surfactants, and the catalysts. For example, rigid foams are made with relatively high functionality isocyanates and polyols, while open cell foams, particularly flexible open cell foams, are made with low functionality isocyanates and high molecular weight polyols which can include both diols and triols.
Accordingly, the need still exists for a process for producing an open cell polyurethane foam which is free of traditional, hazardous blowing agents.
Thus, it is an object of the present invention to provide a blowing agent which does not have the environmental and health hazards associated with methylene chloride and chlorofluorocarbons.
It is a further object of the present invention to provide a process for the production of open cell polyurethane foam utilizing such blowing agent.
These and further objects will become apparent from the specification and claims which follow.